Biometric authentication techniques rely on biometric features inseparable from a person. Hence, they are said to involve lower risks of theft and forgery than identity verifications based on a person's memory, such as a personal identification number or a password, or identity verifications based on objects, such as a seal or a card. However, a possibility of “spoofing” has been pointed out in which a third person fraudulently obtains a biometric feature and completes authentication using a counterfeit of the feature.
Accordingly, to achieve a high security level with biometric authentication, it is necessary to determine whether an object observed to obtain a feature is a biological body or is a counterfeit (non-biological body). For this, various techniques have been disclosed.
In a known technique, a finger is irradiated with spot-like light of linearly polarized light, and reflected light is polarization-separated to determine whether the object is a biological body in accordance with the ratio between surface-reflected light and internally diffused light (see, for example, Japanese Laid-open Patent Publication No. 2-79181). A known biometric authentication apparatus is capable of switching between vein authentication and fingerprint authentication (see, for example, Japanese Laid-open Patent Publication No. 2010-218259).
The conventional technique relying on spot-like light to determine whether an object is a biological body is based on the premise that reflected light from the spot-like light is incident on a detector. However, in a case where a palm is an object to be detected, surface-reflected light does not necessarily accurately reach the detector because the palm has a complicated concavo-convex shape and the posture is unstable when the hand is held over the detector in a noncontact manner. This may cause a problem wherein it is not correctly determined whether an object to be detected is a biological body.